Anaerobic exercise is complementary to aerobic exercise. The early stage of all exercise is anaerobic.

Introduction

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Anaerobic means "without air", and refers to the energy exchange in living tissue which is independent of oxygen. Anaerobic exercise is brief, high intensity activity where anaerobic metabolism is taking place in muscles. During extended periods of exercise aerobic metabolism supplies the bulk of the energy and the exercise is termed aerobic exercise.

Examples of anaerobic exercise include weight lifting, sprinting, and jumping; any exercise that consists of short exertion is an anaerobic exercise. Anaerobic exercise is typically used by athletes in non-endurance sports to build power and by body builders to build muscle mass. Muscles that are trained under anaerobic exercise develop biologically differently giving them greater performance in short duration-high intensity activities.

Aerobic exercise, on the other hand, includes lower intensity activities performed for longer periods of time. Activities like walking, running, swimming, and cycling require a great deal of oxygen to make the energy needed for prolonged exercise.

Anaerobic biochemistry

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Anaerobics are activities that are carried out 'without oxygen'. This terminology refers to the molecular level of respiration, not the respiration of the organism as a whole (i.e., breathing). During anaerobic exercise, the muscles being exercised have insufficient oxygen to meet the demands of the activity, and thus must also use alternate, non-oxygen-dependent processes to produce energy. The muscle does still receive oxygen during anaerobic exercise; the average drop in blood oxygen content throughout the body is likely minimal.

Anaerobic exercise begins with muscles utilizing stored creatine phosphate to generate the ATP that produces muscle contraction. After several seconds, further ATP energy is made available to muscles by metabolizing muscle glycogen or sugars in the blood to lactate. The following aerobic phase is limited by the ability of the heart and lungs to supply the muscle with oxygen. Aerobic metabolism can utilise carbohydrates or fats, as well as lactic acid from anaerobic metabolism, as fuel, releasing larger amounts of energy.

Anaerobic threshold

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The anaerobic threshold (AT) is the exercise intensity at which lactate (lactic acid) starts to accumulate in the blood stream. This happens when it is produced faster than it can be metabolized. This point is sometimes referred to as the lactate threshold, or the onset of blood lactate accumulation (OBLA). When exercising below the AT intensity any lactate produced by the muscles is removed by the body without it building up.

The anaerobic threshold is a useful measure for deciding exercise intensity for training and racing in endurance sports (eg distance running, cycling, rowing, swimming and cross country skiing).

Accurately measuring the anaerobic threshold involves taking blood samples (normally a pinprick to the thumb) during a ramp test where the exercise intensity is progressively increased. Measuring the anaerobic threshold can also be performed non-invasively using gas-exchange methods, which requires a metabolic cart to meaure air inspired and expired.

Although the anaerobic threshold is defined as the point when lactic acid starts to accumulate, some testers approximate this by using the point at which lactate reaches a concentration of 4 mM (at rest it is around 1 mM).

Exercise physiology